Masterclass: Illustrator CS4's Blob Brush

Add creative blobs to your Illustrator sketches.

By
Karl Hodge
| 22 Apr 09

Illustrator is the vector imaging package in Adobe Creative Suite 4, the must-have bundle for web and graphic designers. One of the most interesting new features in CS4 is the Blob Brush, a tool that enables you to directly paint filled paths.

Offering freehand control over vector illustration, the Blob Brush helps you create images with a human touch. It fits easily into your work flow, generating vector paths that can be tweaked using traditional tools. Blobs can be changed using the Warp tool or the Eraser, and Beziér curves allow for precision path edits. In this tutorial we take you through the major features of the Blob Brush, from simple drawing to final refinement.

1. Painting by numbers Download the file blobapple.jpg from http//:tiny.cc/upf9s. We’ll be painting over this bitmap, making a vector version. Open the Layers panel by going to Window?Layers or hitting F7. Name the new layer “flat apple”. Click the Eyedropper tool in the toolbox and select some of the green in the apple image.

2. Fill function With the “flat apple” layer active, select the Blob Brush tool. Paint the entire area of the apple with the selected green colour. As you paint, you’ll notice that your strokes are automatically converted to a fill path and smoothed out. Any stroke you make with the same colour is added to the path.

3. Size matters You can quickly change the size of your brush as you paint use the square bracket keys. Don’t worry about how accurate your coverage of the apple is – you’ll clean that up at a later stage. The important thing is that the entire area is filled with colour.

4. Smooth mover You can edit paths drawn with the Blob Brush just like bitmap fills. If you have any overlaps in the fill you’ve applied, choose the Eraser tool and remove the excess. As you erase the fill looks like a bitmap, with jagged and pixelated edges. When you’re done, the vector path is redrawn and smoothed out.

5. Refine and define You can further refine your artwork using the standard path-editing tools – because the Blob Brush generates standard paths. Here’s a tip before you start: select the vector object you drew with the brush and turn the opacity of the object down to 50 per cent in the toolbar.

6. Creating contours Now you can see through to the layer below. Choose the Direct Selection tool, which enables you to change the position of anchor points and move Beziér handles to change the curve of the object’s path. It should be an easy job to make the vector shape fit more accurately to the contours of the image.

7. Lumps and bumps Drawing with the Blob Brush can give quite bumpy results, but you can use the Smooth tool – in the same section as the pencil tool. With the object and its path selected, draw over the section you want to smooth and refine the results by clicking Command to switch to the Direct Selection tool.

8. Fine tuning The Blob Brush can be used to achieve fine results in tandem with a graphic tablet. To add highlights start a new layer then double-click on the toolbox Blob Brush icon to open its settings. Under Default Brush Options select Pressure from the Size drop-down and about 20pt in the variation slider.

9. Colouring in Select a new colour with the Eyedropper tool and paint in the finer details, such as highlights and blemishes. You’ll notice that even though you’re painting directly over the previous blob, the paths aren’t joined. The tool is colour dependent, so blobs with new colour are treated separately.

10. Know your limits On the automatic merging properties of the Blob Brush, it’s worth pointing some of its limitations. If you draw two blobs of the same colour, then drag one on top of the other, they won’t automatically merge. However, draw a second blob of the same colour on an existing one, and they will merge.

11. Be selective You can set the Blob Brush to only merge new strokes with selected items. Double click on the Blob Brush icon to open its settings dialog and check Selection Limits Merge. Now, draw a few separate blobs, selecting only one. When you draw over the top of these, only the selected object is merged.

12. Merging matters Illustrator arranges objects in the Z plane, or third dimension, enabling you to overlap them. If you have an object at the bottom of the stack and one at the top of the same colour they can be merged with the Blob Brush. But put a different coloured object between them and merging stops working.

13. Flashback Veterans of Flash may find this workflow familiar. It’s similar to the way Flash’s drawing tools work, but where Flash shapes of differing colours cut and intersect other shapes by default, the Blob Brush tool will only merge strokes of the same colour value.

14. Tidying up The Illustrator Warp Tool functions in a similar way to Flash’s path-editing tools and is an ideal companion to the Blob Brush. Use it to tidy up paths after smoothing and fitting anchor points manually. When you’ve done that, experiment with stroke colours and vector effects to finish off the illustration.